We have previously shown that there is a close correlation of bradykinin levels with renin activity and angiotensin II in studies which acutely suppress or activate the renin-angiotensin system (J Clin Invest 55:691-698, 1975). We would like to test the hypothesis that bradykinin, a potent vasodilator, might be a physiological antagonist of renin-angiotensin system in normal and disease states. By use of established radioimmunoassays we will study this relationship in three main categories of patients (1) Essential hypertension where the plasma renin activity is variable, (2) Cirrhosis of the liver where the plasma renin activity and angiotensin II are raised and (3) Williams' trait where there is total kininogen deficiency and absent plasma bradykinin. Sodium balance in these patients will be altered by dietary regulation, I.V. saline infusion and use of diuretics during the study.